1. Field of the Invention
The present invention relates to a lens barrel for a camera, and more particularly to a mounting structure of a flexible printed board which is mounted in a lens barrel for a camera.
2. Description of the Related Art
FIG. 16 is a schematic sectional view showing a mounting structure of a flexible printed board (also referred to as a “flexible board”) for electrically connecting, to a camera body, a shutter, a diaphragm, a focusing mechanism, etc., which are disposed within a known retracting zoom lens barrel, and FIG. 17 is a schematic view of the zoom lens barrel from the front side.
Referring to FIG. 16, the zoom lens barrel comprises a first group unit 101 and a second group unit 102. A shutter and diaphragm unit 103 is attached to the second group unit 102. A rectilinearly moving barrel 104 guides the first group unit 101 and the second group unit 102 in the direction of an optical axis. A cam barrel 105 has cam grooves 105a, 105b, and a stationary barrel 106 has a cam groove 106a, a through hole 106b and a slit hole 106c. The holes 106b, 106c are each extended along a similar locus to that of the cam groove 106a. A rotating barrel 107 has a rectilinear groove 107a and a slit hole 107b. Other components include a cover member 108 having a slit hole 108a, a base member 109, a first-group cam follower 110 attached to the first group unit 101, a second-group cam follower 111, a cam barrel follower 112, and a driving pin 113. A flexible board 114 is connected at one end to the shutter and diaphragm unit 103 and at the other end to a flexible board (not shown) on the body side through the slit holes 106c, 107b and 108a. 
In the structure described above, when the rotating barrel 107 is rotated by a driving source (not shown), the rotation of the rotating barrel 107 is transmitted from the rectilinear groove 107a to the driving pin 113. Correspondingly, the cam barrel 105 is moved in the direction of the optical axis while rotating along the cam groove 106a, because the cam groove 106a and the cam barrel follower 112 are engaged with each other. With the rotation of the cam barrel 105, the first group unit 101 and the second group unit 102 are also moved in the direction of the optical axis along the cam grooves 105a, 105b, respectively. At this time, the rotating barrel 107 is rotated by a predetermined angle from a retracted position to a position in the WIDE-TELE zoom region. As shown in FIG. 17, the slit hole 107b of the rotating barrel 107 through which the flexible board 114 passes is formed over a circumferential distance corresponding to the angle by which the rotating barrel 107 is rotatable.
The above-described mounting structure of the flexible board for electrically connecting the shutter and diaphragm unit 103, which is disposed within the retracting zoom lens barrel, to the camera body is generally employed with the purpose of minimizing the amount of slack by which the flexible board is loosened into an inner space of the lens barrel when the lens barrel is extended out (i.e., a purpose of eliminating vignetting caused on internal reflection and an effective optical path by the slack of the flexible board in a shooting state).
However, in a lens barrel of the type wherein other units requiring electrical connection to the camera body, such as a focusing unit and an anti-shaking unit, are also attached to the second group unit 102 within the lens barrel in addition to the shutter and diaphragm unit 103, the above-described known structure has disadvantages in that the width (indicated by a in FIG. 17) of the flexible board is increased and the outer dimension of the lens barrel is enlarged. When the flexible board is divided into two parts and each board is mounted with the above-described known structure, the angle (indicated by b in FIG. 17) of the slit hole is increased two folds corresponding to the divided two flexible boards. Therefore, the strength of the rotating barrel 107 as one of the lens barrel components cannot be ensured at a sufficient level.